Anatomy of the Ear Flashcards
3 parts of the ear
- External
- Middle
- Internal
2 main parts of the external ear
- Auricle/pinna
- External acoustic meatus (ear canal)
What separates the external ear from the middle ear?
Tympanic membrane
Innervation of auricle
- More superficial surfaces: greater auricular nerve (C2, C3), lesser occipital nerve (from cervical plexus), auriculotemporal branch of mandibular nerve (CNV3)
- Deeper parts: auricular branch of vagus nerve, facial nerve
Innervation of auricular muscles
Facial nerve (CNVII)
Parts of the auricle
Helix, antihelix, tragus, antitragus, concha, lobule
To inspect the tympanic membrane, in which direction does the doctor have to pull the pinna? Why is this necessary? What features of the EAM permit the movement?
- Superiorly, posteriorly & slightly laterally because the EAM does not follow a straight course
- To reduce the curvature of the EAM, facilitating insertion of otoscope
- The lateral third of the EAM is cartilaginous making it flexible
EAM contains modified sweat glands that produce __
cerumen (earwax)
Sensory innervation of EAM
Major input from auriculotemporal branch of CNV3 & auricular branch of CNX
2 parts of the middle ear
- Tympanic cavity (immediately adjacent to TM)
- Epitympanic recess (superiorly)
The middle ear communicates with __ posteriorly and __ anteriorly.
- mastoid area
- nasopharynx (via pharyngotympanic tube)
3 auditory ossicles
- Malleus (largest)
- Incus
- Stapes (most medial)
What is the stapes connected to?
Connected to incus by synovial joint & attached to lateral wall of internal ear at oval window
2 muscles associated with auditory ossicles
- Tensor tympani
- Stapedius
Innervation of tensor tympani
Mandibular branch of trigeminal nerve
Innervation of stapedius
Branch of facial nerve
What does contraction of the tensor tympani muscle do?
It pulls the handle of the malleus medially, tensing the tympanic membrane. It mainly reduces vibration amplitude, protecting the inner ear.
What does contraction of the stapedius muscle do?
It pulls the stapes posteriorly, preventing excessive oscillation and therefore damage to the inner ear.
Parts of the malleus
Head, neck, anterior & posterior processes, handle
Parts of the incus
Body, long & short limbs
Parts of the stapes
Head, anterior & posterior limbs, base
6 boundaries of the middle ear
- Roof (tegmental wall)
- Floor (jugular wall)
- Anterior wall
- Posterior (mastoid) wall
- Lateral (membranous) wall
- Medial (labyrinthine) wall
What separates the middle ear from the middle cranial fossa?
Tegmen tympani
What enters the middle ear through a small aperture near the medial border of the floor?
Tympanic branch of glossopharyngeal nerve
Innervation of the middle ear
Tympanic plexus = tympanic branch of CNIX + branches of internal carotid plexus
Why can infections in the middle ear easily spread into the mastoid area?
Because the mucous membrane lining the mastoid air cells is continuous with the mucous membrane throughout the middle ear
Why is it extremely important not to damage the mastoid wall of the middle ear?
To prevent injury to the facial nerve
What is a frequent complication of mastoiditis?
Meningitis
What is the tympanic membrane made up of?
Connective tissue core with skin on outside & mucous membrane on inside
What is the name of the attachment to the handle of the malleus on the tympanic membrane?
The umbo
2 main parts of tympanic membrane
Pars flaccida & pars tensa
Innervation of TM
- Skin: auriculotemporal branch of CNV3, auricular branch of CNX
- Mucous membrane: CNIX
Infection of middle ear
Otitis media
Untreated otitis media can lead to…
- Perforated tympanic membrane
- Hearing loss
- Meningitis
- Brain abscess
What is Swimmer’s ear?
Otitis externa (infection in external acoustic meatus)
What is cauliflower ear?
Subperichondrial hematoma - deformity caused by blunt trauma to auricle
What is Surfer’s ear (exostoses)?
- Development of a ‘bony lump’ in EAM usually resulting from cold water
- Growth of the lump eventually constricts EAM & reduces hearing.
What is the name for the disorder, sometimes hereditary, in which there is formation of new bone around the base of the stapes? What does this result in?
- Otosclerosis
- Progressive hearing loss
What is acoustic neuroma?
Also know as vestibular schwannoma - benign, slow-growing tumour along vestibulocochlear nerve
What is a cholesteatoma?
Abnormal, non-cancerous skin growth that forms behind tympanic membrane or from tympanic membrane
How is the middle ear & internal ear investigated?
By CT or MRI
What does the internal ear consist of?
- Bony labyrinth (3 semicircular canals, vestibule, cochlea)
- Membranous labyrinth (semicircular ducts, utricle & saccule, scala vestibuli, scala tympani, scala media)
Organs of balance
Semicircular duct, utricle & saccule
Organ of hearing
Cochlear duct (scala media)
Which ducts contain perilymph?
Scala vestibuli & scala tympani
Which duct contains endolymph?
Scala media
CNVIII divides into vestibular and cochlear parts after entering the __
internal acoustic meatus
Site of Organ of Corti
Basilar membrane
Cell types in Organ of Corti
- Inner hair cells
- Outer hair cells
- Auditory sensory cells
